Heating furnace

ABSTRACT

A heating furnace comprising a hearth which includes charge supporting members each comprised of an upper tubular member and a lower tubular member connected together by an intermediate tubular member to form a rigid, water cooled truss. The furnace may be divided into a series of heating zones by top and bottom partitions from which the furnace is end fired. In one embodiment a first series of trusses is movable longitudinally while a second series of trusses is alternately movable vertically to convey a charge through the furnace. Alternatively, certain of the trusses may be fixedly mounted, while others are mounted for movement both longitudinally and vertically in the furnace. The trusses are supported at each bottom partition with the movable trusses being mounted on a carriage which is movable in and forms a traversing seal over a slot in the bottom partition. A reverse fired bottom soaking zone and a downtake flue adjacent the discharge end of the furnace insure heating of the charge by hot gases until discharge. Another embodiment includes charge supporting members movable both longitudinally and vertically in the furnace and constructed of two sections connected together to permit independent relative vertical movement with respect to each other to cause closely packed charges on the first section to become spaced as they move to the second section. A downtake flue positioned in a preheat zone underneath the first section draws hot gases over the top of the charges on the first section towards the charge end of the furnace and back underneath the charges to heat the bottom.

United States Patent 1 1 Anderson HEATING FURNACE [75] Inventor: Robert James Anderson, Pittsburgh,

[73] Assignee: Rust Furnace Company, Pittsburgh,

[22] Filed: Feb. 23, 1971 [21] Appl. No.: 118,027

(52] US: Cl. 432/133,

1 37, 146, 241 244 234 243 [51] Int. Cl ..F27b 9/14 [58] Field of Search ..263/6 R, 6 A, 6 B, 36, 44

[56] References Cited UNITED STATES PATENTS 1,680,468 8/1928 Menne ..263/6 R 3,623,715 ll/l97l Costick ..263/36 2,017,024 10/1935 Cochran et a1.

Primary Examiner-John J. Camby Attorney-Birch, Swindler, McKie & Beckett [57] ABSTRACT A heating furnace comprising a hearth which includes charge supporting members each comprised of an upper tubular member and a lower tubular member connected together by an intermediate tubular 1 Feb. 13,1973

member to form a rigid, water cooled truss. The furnace may be divided into a series of heating zones by top and bottom partitions from which the furnace is end fired.

In one embodiment a first series of trusses is movable longitudinally while a second series of trusses is alternately movable vertically to convey a charge through the furnace. Alternatively, certain of the trusses may be fixedly mounted, while others are mounted for movement both longitudinally and vertically in the furnace. The trusses are supported at each bottom partition with the movable trusses being --mounted on a carriage which is movable in and forms a traversing seal over a slot in the bottom partition. A reverse fired bottom soaking zone and a downtake flue adjacent the discharge end of the furnace insure heating of the charge by hot gases until discharge.

Another embodiment includes charge supporting members movable both longitudinally and vertically in the furnace and constructed of two sections connected together to permit independent relative vertical movement with respect to each other to cause closely packed charges on the first section to become spaced as they move to the second section. A downtake flue positioned in a preheat zone underneath the first section draws hot gases over the top of the charges on the first section towards the charge end of the furnace and back underneath the charges to heat the bottom.

27 Claims, 15 Drawing Figures PAIENTEU ram 3192a SHEET 2 OF 9 FIG. 3 7

INVENTOR. ROBERT J. ANDERSON AT TOR N EYS.

PATENTED FEB] 3 I973 SHEET 3 OF 9 FIG. 4

INVENTOR. ROBERT J. ANDERSON Qua-4v, ,JfZM BY W 64m 32 r-l nnnnnn/nn/n ATTORNEYS.

PATENTEBFEBIBIQYS Y 3,716,222

SHEEHUF 9 FIG. 6

INVENTOR. ROBERT J. ANDERSON ATTORNEYS PAIENTEDFEB 13 I975 SHEET 5 0F 9 FIG. 7

INVENTOR ROBERT J. ANDERSON FIG. 8

ATTORNEYS.

PATENTEUFEB 13 I975 SHEET 9 BF 9 FIG. l4

FIG. l3

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INVENTOR ROBERT J. ANDERSON ATTORNEYS.

HEATING FURNACE BACKGROUND OF THE INVENTION for hot working operations wherein it is desirable to obl0 tain even heating throughout the charge without prolonged soaking in the furnace.

2. Description of the Prior Art Large bodies of metal, such as billets, slabs, blooms, and the like have generally been heated in multizone pusher type furnaces wherein the zones are arranged to provide top and bottom heating. The material is pushed over a network of water cooled beams or support pipes. This has not proved entirely satisfactory, however, in that skid marks are left in the metal surface as the result of the sliding contact between the metal and the water cooled support skids.

Movable hearth or walking beam type furnaces have also been used to heat large bodies of metal wherein the charge or workpiece is alternately lifted, indexed forward and then supported on a fixed part of the hearth while the movable portion of the hearth is retracted in preparation for the next cycle. Other walking beam type furnaces also have been used wherein the charge is moved forward a short distance by one set of beams, then lifted on another set of beams while the first set of beams retracts, and finally set back down on the first set of beams wherein the cycle again is repeated to index the charge through the furnace.

In furnaces of this type, however, the mechanism comprising the movable hearth has made it difficult to provide a satisfactory furnace wherein the charge is heated from the bottom as well as from the sides and the top. Consequently, it has been necessary to heat the charge a longer period of time in an effort to obtain a uniform temperature throughout the charge. Efforts to construct walking beam type furnaces to provide suitable bottom firing as well as top and side firing have experienced difficulty in constructing a suitable support system which provides sufficient strength to securely support and move a charge through the furnace while at the same time permitting an even application and distribution of heat to the underside of the charge.

Difficulty has also been encountered in prior movable hearth or walking beam furnaces in providing an effective seal at the points where the structure supporting the hearth passes through the bottom of the furnace. A further problem with prior art furnaces has been to prevent cold air from infiltrating through the discharge opening and causing uneven temperatures in a charge prior to itsbeing discharged.

SUMMARY OF THE INVENTION span relatively long distances without additional support intermediate of the ends.

According to the present invention there is provided a heating furnace comprising a charge supporting hearth which includes charge supporting members each comprised of an upper tubular member, a lower tubular member and at least one intermediate tubular member extending between and connected to the upper and lower tubular members to form a rigid water-cooled truss.

In one embodiment of the invention the trusses are supported by a plurality of spaced bottom partitions extending upwardly from the bottom of the furnace to define a series of bottom heating zones. The furnace is end tired from burners mounted in the bottom partitions. A first series of advancing trusses are supported on the bottom partitions by carriages movable endwise on the partitions in slots whereby the carriages form a traversing seal with slots. A second series of lifting trusses are mounted on the bottom partitions for alternating vertical movement to advance a charge stepwise through the furnace.

Alternatively a first series of trusses or support pipes may be fixedly mounted on the bottom partitions and a second series of trusses supported on the bottom partitions by similar carriages are mounted for movement both longitudinally and vertically to advance a charge stepwise through the furnace. In a further embodiment a reverse fired bottom soaking zone and a downtake flue are provided adjacent the discharge end of the furnace, to direct heat in the direction of travel of the charge in the zone and to cause hot waste gases to heat the charge until it is discharged from the furnace.

Another embodiment of the invention comprises a charge supporting hearth which includes a plurality of movable charge supporting members each comprised of a first section and a second section connected together and mounted formovement both longitudinally and vertically in the furnace. The two sections are connected together to permit independent relative vertical movement with respect to each other. The first section is comprised of an upper tubular member and a lower tubular member connected together by at least one intermediate tubular member to form a rigid watercooled truss. The hearth also includes fixed supports whereby the movable supports lift and advance the charges to convey them stepwise through the furnace. The furnace includes a preheat zone through which the first of closely packed charges in the zone towards the charge end of the furnace and then back down underneath the charges to heat the bottoms thereof.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the invention will become apparent by reference to the detailed description of the invention and the accompanying drawings which follow, wherein:

FIG. 1 is a longitudinal sectional view of a heating furnace constructed according to the principles of the present invention;

FIG. 2 is a partial top sectional plan view of the furnace taken along line 2-2 of FIG. 1;

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 1;

FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 3, showing the ends of two advancing trusses;

FIG. 5 is an enlarged cross-sectional view of the discharge end of the furnace of FIG. 1, illustrating the mechanism for moving the advancing trusses;

FIG. 6 is an enlarged longitudinal sectional view of an end of a furnace, illustrating a further embodiment of the furnace of the present invention;

FIG. 7 is a cross-sectional view taken along line 77 of FIG. 3 showing the ends of two lifting trusses;

FIG. 8 is a cross-sectional view of a further embodiment of the invention showing two fixed trusses mounted on top of a bottom partition;

FIG. 9 is a cross-sectional view of another embodiment of the invention showing two trusses movable both longitudinally and vertically, mounted on a bottom partition;

FIG. 10 is a view taken along line 10-10 of FIG. 9;

FIG. 11 is a partial top sectional plan view of a further embodiment of a heating furnace constructed according to the principles of the present invention;

FIG. 12 is a longitudinal sectional view of the heating furnace of FIG. 1 1.

FIG. 13 is a cross-sectional view taken along line l313 ofFIG. 12;

FIG. 14 is a cross-sectional view taken along line 14l4 of FIG. 12; and

FIG. 15 is a front elevational view taken along line l515 ofFIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 thru 5 of the drawings, there is shown in section a heating furnace 11 having an entry or charging end 12 and an exit or discharge end 13. The furnace is divided into a plurality of heating zones lengthwise thereof by a plurality of correspondingly spaced top and bottom partitions 21 and 22 respectively, extending transversely of the furnace across the entire width thereof. The bottom partitions extend upwardly from the base of the furnace and the top partitions extend downwardly from the top of the furnace.

In the embodiment illustrated in FIG. 1, the furnace is divided into top and bottom primary or preheating zones 14 and 15, respectively, top and bottom secondary heating zones 16 and 17, respectively, and top and bottom soak zones 18 and 19, respectively. The furnace is heated by bottom end burners 23 mounted in walls of the bottom partitions 22 and top end burners 24 mounted in the walls of top partitions 21. The bottom and top end burners 23 and 24 are mounted to discharge heat towards the charging end of the furnace in a direction opposite to that in which the charge or work being heated flows through the furnace.

As shown in FIGS. 1 and 3, the top and bottom end burners 23 and 24 are spaced in the partitions across the width of the furnace to provide an even heat both above and below the charge throughout the width of the furnace. Top soak zone 18 is heated by a plurality of conventional burners 25 mounted in the roof of the zone to discharge heat downwardly into the zone. If desired top soak zone 18 also may be heated by end burners.

While the furnace of the present invention operates satisfactorily using just the top and bottom end burners and the roof burners in the soak zone, side burners also may be employed if desired. By providing burners in each zone, the temperature may be controlled with respect to each zone, as desired. The burners may be of standard design and may use either hot or cold air. The furnace is provided with a waste gas collector 26 at its charge end for the exit of waste gases from the furnace. Waste gas collector 26 is connected to a stack by a flue in a conventional well known manner. The flue may be equipped with a recuperator to utilize the flue gas to preheat the combustion air. Alternatively, the flue gases may simply be discharged to the atmosphere or used in any other appropriate manner.

The charge 20 or work being heated is advanced longitudinally endwise through the furnace from the charge end to the discharge end by a movable hearth indicated generally by the numeral 31. The hearth is constructed of a plurality of advancing trusses or frames 32 and lifting trusses or frames 33, each of which is water-cooled.

As shown in FIGS. 1 to 4 and 7, each individual truss is comprised of an upper tubular member or pipe 34 which is straight throughout its length to provide a support for a charge in the furnace, a lower tubular member or pipe 35, a first intermediate tubular member or pipe 36, a second intermediate tubular member or pipe 37 and a third intermediate tubular member or pipe 38. Each upper pipe 34 is provided with a plurality of spaced support buttons or bars 39 for supporting the charge being heated in the furnace. These support buttons may be constructed of a chromium-nickel alloy material welded on top of the pipes. All of the pipes are connected together at spaced locations to form a rigid load bearing truss of great strength. Lower tubular member 35 of each truss is generally V shaped in configuration whereby it is lower at the center point than at either end. All of the pipes are covered with a suitable insulation material.

Pipe 36 extends from one end downwardly to pipe 35 and then upwardly to pipe 34 and then continues in a serpentine fashion to extend between lower pipe 35 and upper pipe 34 throughout the length of the truss to rigidly connect the upper and lower pipes together at spaced intervals. Intermediate pipe 37 extends from one end of the truss as shown in FIG. 1 and connects intermediate pipe 36 and upper pipe 34 at spaced locations for a portion of the length of pipes 34 and 36. Similarly on the opposite end of the truss, pipe 38 extends from one end thereof to various positions between pipe 34 and pipe 36 to connect the two pipes for a portion of their length. If the truss 32 is a single truss, the ends of pipes 37 and 38 are connected together to form a path for the continuous flow of water from one end to the other. If two advancing trusses 32 are connected together to form a rigid unit as shown in FIG. 3, pipes 37 and 38 then cross over and extend between the two trusses to rigidly connect the upper portions of the two trusses together. Thus the trusses provide an open rigid framework which greatly facilitates the application of heat to all parts of a charge.

As shown in FIG. 7, the lifting trusses 33 have the same general configuration of pipes as the advancing trusses 32, except that the ends of the top pipe 34 on each lifting truss extend outwardly at the top and then curve back down underneath to extend into the support structure to be described more fully hereinafter.

In the embodiment of the invention shown in FIGS. 1 through 7, the end truss is a single lifting truss, whereas the remaining trusses between the ends are comprised of pairs of advancing trusses connected together and alternating with pairs of lifting trusses connected together as shown in FIG. 3. Thus the advancing trusses 32 and lifting trusses 33 are alternately spaced in pairs across the width of the furnace in interdigitated fashion.

Each pair of advancing trusses 32 of movable hearth 31 is movably supported for longitudinal movement endwise of the furnace at each bottom partition 22 by a carriage or bearing section 41, comprised of a suitable refractory material. As shown in FIGS. 3 and 4 each carriage 41 is provided on its bottom with a framework 42 of hollow tube: which extend around the inside outer edges of the carriage as well as across the width in the center of the carriage. The individual pipes of each truss are connected to the framework 42 to not only supply rigidity to the end of the truss, but also to function as means for supplying water or other cooling fluid to the pipes of the trusses. Water is supplied to the framework 42 by suitable connecting means.

Referring to FIGS. 3 and 4, it will be seen that carriage 41 is movably supported on the bottom partitions 22 by rollers 43 mounted in bearings fastened to horizontal beams 51 which in turn are supported by stationary columns 52.

Each carriage 41 operates longitudinally through a slot 44 cut into the refractory covering on the top of the bottom zone partition 22. It is to be noted that the carriage 41 is sufficiently large to overlap the edges of each slot 44 to provide a close fitting traversing horizontal seal which will prevent scale from dropping into the mechanism and structure below the top of the partition as well as to prevent heat from the furnace from escaping out through the partitions. Moreover, the seal formed by the carriage minimizes the amount of cold air infiltrating into the interior of the furnace through the partitions. As also shown in FIG. 4, each carriage 41 is longer by a predetermined distance than the length of each slot 44 to permit longitudinal movement of the carriage endwise of the furnace without exposing any portion of the slot. Each slot 44 is provided with a water-cooled tubular frame 45 around its upper edges.

Referring to FIG. 7, each lifting truss, as previously noted, is also comprised of a plurality of individual pipes which come together at their ends and are rigidly connected by a sleeve 46. The ends of the pipes of each lifting truss as well as sleeve 46 extend through an alloy sleeve 47 in a slot 48 in bottom partition 22. Sleeve 47 extends above the top of bottom partition 22 and into a cover 49 extending over the pipes of the truss. The cover 49 and sleeve 47 function as a seal to prevent scale from falling into the structure below. A bracket 50 attached to the pipes of each lifting truss below the pipe sleeve 46 is connected to a rigid frame 53 constructed of intersecting beams running longitudinally along the furnace length and traversely across the width beneath the bottom zone partitions. Frame 53 is vertically movable by means to be described later to move the lifting trusses vertically through sleeve 47 in each bottom partition 22. The ends of the pipes of each lifting truss are connected to water-supply means or other suitable cooling fluid.

As shown in FIG. 3, the frame 53 is supported by wide flange columns 54 and tubular side columns 55 which are free to move vertically through the core of stationary columns 52. Columns 52 are securely mounted at the bottom of the furnace as shown in FIG. 3 and may be cross-braced to insure lateral stability of the furnace structure. The wide flange columns 54 constitute the main vertical support members for the frame 53. The tubular side columns 55 are restrained by suitable guides or bearings 56 fastened to columns 52 to permit motion only in a vertical direction.

Both movable columns 54 and 55 are rigidly fastened at their lower ends to lift beams 61, spaced inside on either side of the bottom partitions 22 and extending transversely of the furnace, as shown in FIGS. 3 and 4. Each lifting beam 61 is supported on rollers 62 mounted on bell cranks 63. The bell cranks are connected by a tension rod 64 attached to a rocker arm 65 which, in turn, is connected to suitable power means such as hydraulic cylinder 66. Hydraulic cylinders 66 are provided at each bottom partition to furnish lift along the length of the furnace. The cylinders may be powered by a common pump and synchronized by known means to provide for an even lift along the length of the furnace. While a hydraulic drive system is shown in the drawings, it will be appreciated that a suitable mechanical drive system may also be used such as eccentrics and crank arms driven by suitable motor means.

Advancing trusses 32 may be driven from the discharge end of the furnace as shown in FIGS. 1 and 5, by hydraulic cylinders 67 connected directly to the underside of the carriage 41 at the discharge end of each advancing truss by suitable bracket means 68. A plurality of such cylinders are provided which may be driven by a common pump and synchronized to provide a simultaneous, even longitudinal motion endwise of the furnace of all the advancing trusses.

The bottom fired area of the furnace is divided into zones of equal length, as illustrated in FIG. 1. This permits the individual trusses to be constructed such that one truss section spans each zone, thus permitting greater uniformity of parts for easier maintenance and repair.

The furnace may be provided with side observation doors located below the elevation of the advancing trusses. This location permits the furnace to be operated at positive pressure below the material support line and near zero to slightly negative pressure at the traversing seal effected by the carriages on the top of each partition. These near-atmospheric pressures at this elevation will minimize the amount of air infiltration around the traversing carriage seal without causing excessively high pressure at the observation door.

In the operation of the embodiment of the invention shown in FIG. 1 through 5 and 7, the charge 20 to be heated is transferred to the movable hearth at the entrance of the furnace by any suitable means. As the furnace commences operation and the advancing and lifting trusses comprising the movable hearth begin to move, the lifting trusses 33 are initially in a down position and the charge is supported only by the advancing trusses 32 which are in a retracted position. When a work cycle is initiated, the advancing trusses travel forward a preset distance and stop, whereupon the lifting trusses are then raised to remove the charge from the advancing trusses. The advancing trusses then retract to their original position, at which time the lifting trusses then lower the charge back on to the advancing trusses and the cycle is again repeated to move the charge endwise through the furnace in a step-by-step movement. During operation of the furnace, the material or charge is advanced therethrough in a direction opposite that to which the heated gases flow through the furnace. The hot waste gases move towards the entry end of the furnace to be discharged through the waste gas collector 26.

During operation of each work cycle, the lifting trusses operate continuously at a constant speed with a vertical motion which is divided equally above and below the elevation of the advancing trusses. This method of operation alternates points of material support between the lifting and advancing trusses and exposes each support point on the charge to direct furnace heating for half the time the charge is in the furnace. This is highly advantageous in that it minimizes or eliminates any temperature differences between the points at which the charge is supported and the remainder of the charge. All heat is thus transferred substantially evenly to all of the surfaces of the charge. The use of trusses as charge supporting members in the furnace greatly enhances the even transfer of heat to all surfaces of the charge, since the trusses provide an open framework underneath the charge which permits greater exposure to the heat.

In operation of the furnace of the present invention to reheat, for example, a steel slab, a typical temperature for the top and bottom primary zones would be 2500 F., a typical temperature for the top and bottom secondary zones would be 2400 F., while a typical temperature for the top and bottom soak zones would be 2375 F. A charge normally would travel through the furnace at a rate of 30 to 70 ft. per hour.

Another embodiment of the furnace of the present invention is shown in FIG. 6 which incorporates an additional soak zone. In the embodiment of FIG. 6 a primary soak zone 18A is provided over bottom partition 22 ahead of the top soak zone 18. The primary soak zone 18A is formed by an upper partition 71 extending downwardly from the roof of the furnace.

In the arrangement of FIG. 6 the bottom soak zone 19 is reversed from the other bottom zones to permit it to be reverse fired by end burners 72 directed in the same direction and generally parallel to the path of travel of the work through the furnace. Both the primary top soak zone 18A and the top soak zone 18 are heated by burners mounted in the roof of the furnace. The location of the primary top soak zone 18A is such that the waste gas from this zone is discharged into the top secondary zone 16 from where it moves toward the charging end of the furnace. Waste gas from top soak zone 18 is discharged along with the flue or waste gas from bottom soak zone 19 into a downtake or flue 73 provided adjacent the discharge end 13 of the furnace.

Flue 73 is operated at a negative pressure to induce the flow of heated flue gases from the soak zones 18 and 19 adjacent the discharge end of the furnace across the leading edge of the charge passing therethrough. It is to be noted that the ends of the trusses at the discharge end of the furnace extend out over the flue 73. The flue also causes any cold air which infiltrates through the discharge end to be drawn therein before contacting the heated charge passing through the furnace. The waste gases may be discharged from the flue 73 through a separate stack. A plurality of waste gas flues or downtakes may be constructed across the width of the furnace in such a manner that the advancing truss cylinders can be mounted between the flues. The flues 73 are located between the discharge end 13 of the furnace and the bottom soak zone 19 at a level below that of the movable hearth 31.

The purpose of reverse firing the bottom soak zone and discharging gas at the discharge end of the furnace is to draw the cold air which would normally infiltrate through the furnace discharge door directly down into the flues and out the stack while hot gases continue to pass over the charge. This will insure that the charge in the furnace is completely surrounded by hot gas until it is discharged.

A further embodiment of the invention is shown in FIGS. 9 and 10 wherein the furnace is similar in design to the embodiment of FIGS. 1 through 7, except the hearth is constructed of insulated fixed or stationary supports alternating with insulated trusses movable both longitudinally and vertically in the furnace to convey a charge stepwise therethrough. The fixed support may be a truss, constructed in the manner of advancing trusses 32 previously described, except that the truss is fixedly mounted at its ends on a bottom partition in the manner shown in FIG. 8 to be described more fully hereinafter. Alternatively, the fixed support may be constructed from an individual tubular member or pipe 81 supported by vertical support pipes 82 extending upwardly from the bottom of the furnace and from the bottom partitions at spaced locations throughout the length of the furnace. This latter fixed support is similar in construction to that used in existing pusher type furnaces.

FIG. 10 illustrates fixed water cooled support pipes 81 alternating with pairs of connected water cooled trusses 83 movable longitudinally and vertically. The trusses 83 are similar in construction to the lifting trusses 33 previously described. As shown in FIG. 10, two trusses 83 are connected together by intermediate pipes 38 extending therebetween to form a rigid unit. The ends of each pair of trusses 83 pass through a refractory covered carriage 41 which is movable longitudinally in and over a slot 44 in each bottom partition 22 n a manner similar to that previously described with the embodiment of FIGS. 1 through 7.

The ends of the individual pipes of each truss 83 are rigidly connected together by a sleeve 46 vertically movable through an alloy sleeve 47 extending through and above the top of carriage 41. A cover 49 attached to the pipes forms a seal with sleeve 47 to prevent scale and other debris from falling into the mechanism below the partition.

The pipes of each truss 83 extend downwardly through the carriage 41 and are connected by a bracket 50 to another frame structure or carriage 84. Carriage 84 is positioned for longitudinal movement endwise of the furnace on rollers 43 mounted by suitable brackets and bearings on a frame 53 which is movable vertically by a lifting mechanism similar to that described in the embodiment of FIGS. 1 through 7. The trusses 83 are thus mounted for independent vertical movement through the sleeves 47 in carriage 41 as well as for longitudinal movement endwise of the furnace.

Carriage 41 is of sufficient width and length to extend over the sides as well as the ends of slot 44 to insure a horizontal traversing seal with the slot during longitudinal movement of the carriage. Carriage 41 is supported by beams 85 having a lower lip which rests on rollers 86 supported by suitable bearings on a beam 87 attached to the partition 22. The carriage 41 is restrained against vertical movement by brackets 88 secured to beam 87 and extending out over the bottom lip of beam 85 as shown in FIG. to form a guide assembly therewith. The trusses 83 are moved longitudinally by cylinders attached to the furnace structure at the discharge end and connected to carriages 84 at the end in a manner similar to that described with respect to the embodiment of FIGS. 1 through 7.

In operation of the embodiment shown in FIGS. 9 to 10, the cycle is initiated with the charge 20 resting on the fixed supports 81 and the pairs of trusses 83 lowered and positioned towards the discharge end. The trusses 83 are then moved longitudinally towards the charging end of the furnace until they reach a preselected stroke. At this point the trusses 83 are raised upwardly to lift the charge from the fixed support and then are moved longitudinally towards the discharge end until they have reached their forward extreme position. The trusses 83 then lower the charge back unto the fixed supports 81 and continue down to their initial position in preparation for the next cycle. In this fashion the charge is indexed, or moved stepwise through the furnace from the charge end to the discharge end.

Another embodiment of the invention is illustrated in FIG. 8 which discloses a heating furnace in which the hearth is comprised of a plurality of fixed trusses mounted at their ends by a suitable support such as the bottom partitions previously described wit respect to the embodiments of FIGS. 1 through 7. The trusses 91 shown in FIG. 8 are comprised of a plurality of insulated hollow tubular members or pipes rigidly connected together in the same manner as that described with respect to the advancing trusses 32 of the embodiment of FIGS. 1 through 7. In the embodiment of FIG. 8, however, the individual pipes of each truss at their ends are supported by and extend through the refractory upper part of bottom partition 22 and are rigidly connected to a structural steel framework 92 inside the bottom partition. The ends of the pipes of each truss 91 are connected in a conventional manner to a source of water or other cooling fluid. Upper pipe 34 of each truss 91 is provided with a solid wear rod 93 of suitable material to support the charges. The furnace shown in FIG. 8 operates as a pusher-type furnace wherein charges are placed on top of the upper pipes of the trusses 91 and are pushed through the furnace in a known manner conventionally employed on presentday pusher-type furnaces.

A further embodiment of the present invention is illustrated in FIGS. 11 through 15 of the drawings. The furnace of this embodiment includes a charge end 110 and a discharge end 111. The furnace is o the type employing conventional means for charging billets into the furnace at the charge end through a charging opening 121 in the side of the furnace. Similarly, at the discharge end the billets or other charges are removed through a discharging opening 123 in the side of the furnace by conventional mechanism in a well known manner.

Referring to FIG. 12, the furnace is divided into a plurality of upper heating zones. The heating zone adjacent to charge end of the furnace is a primary or preheat zone designated by the numeral 112. Next to the preheat zone 112 is a first heating zone 1 13 formed at the inner end by an upward extension 114 of the top of the furnace and downwardly extending partition 115 at the other end. A second downwardly extending upper partition 116 divides the remainder of the furnace into a second heating zone 117 and a final soak zone 118. The furnace is heated in at least the soak zone and the first and second heating zones by a plurality of roof burners 119. Although not necessarily required for the operation of the furnace, if desired roof burners also may be employed in the preheat zone 112. The furnace is provided with side observation doors 122 located in the side walls of the furnace at the approximate height of the furnace hearth 124.

The hearth is comprised of a plurality of alternating fixed and movable supports which function to move a charge stepwise through the furnace. The fixed supports in the preheat zone 112 and extending partially into the first heat zone 113 at the charge end of the furnace are comprised of a plurality of spaced skid pipes 125 supported by suitable castings 126 mounted on refractory brick support pier walls 127 as shown in FIGS. 11 and 14. The castings 126 distribute the load from the skid pipes evenly over the top of the walls 127. If desired, solid skid rods 128 may be secured as by welding to the tops of the skid pipes 125 to support the charges in the furnace. The skid pipes 125 and supporting pier walls 127 extend from the charge end of the furnace partway into the first heating zone 113.

Beginning from approximately the end of the skid pipes 125 the fixed supports are comprised of solid refractory material as indicated by the numeral 130 in FIG. 13. The refractory material supports 130 extend from midway in the first heat zone 113 to the discharge end 111 of the furnace.

The movable charge supporting members of the hearth are each comprised of a first section and a second section connected together. As shown in FIGS. 11 and 12, the first section of each movable support member is comprised of a truss 131 constructed in a manner similar to the advancing trusses previously described in the embodiment of FIGS. 1 through 7. Thus each truss 131 is comprised of an upper tubular member or pipe 132, a lower tubular member or pipe 133, a first intermediate tubular member or pipe 134 extending between and rigidly connecting pipes 132 and 133, a second intermediate tubular member or pipe 135, extending between one end of pipes 134 and 132 and a third intermediate tubular member or pipe 136 extending between the opposite ends of pipes 134 and 132. Pipes 135 and 136 are connected by a fourth intermediate tubular member or pipe 137 as shown in FIG. 12. The individual pipes are rigidly connected together at spaced intervals throughout their length to form a rigid water-cooled charge-supporting truss. The pipes are covered by suitable insulation material to minimize heat loss. The pipes of each truss 131 are connected to suitable water or other cooling fluid supply means.

The individual pipes comprising truss 131 are rigidly connected together outside of the charge end of the furnace by a sleeve 138. The truss is supported outside the charge end of the furnace by lifting mechanism 139 to be described more fully hereinafter. The ends of all the trusses outside the charge end of the furnace are connected together and stabilized in a horizontal plane by tie beams 129.

The second section of each movable support member is comprised of a movable refractory beam 141. Each refractory beam is provided at its inner end with a slot 142 extending through from the top to the bottom of the beam. As shown in FIGS. 12, 14 and 15, the inner end of each truss 131 is mounted in each slot 142 for vertical movement. Referring to FIG. 12, it will be seen that the inner ends of pipes 132 and 136 of each truss are received in a vertical guide 143 mounted on the beam 144 which supports refractory beam 141. Vertical guide 143 permits the truss 131 to move independently vertically with respect to refractory beam 141 while still connecting the truss and the beam together for joint longitudinal movement assingle unit endwise of the furnace. Since there is no relative longitudinal movement between the truss 131 and the refractory beam 141, the slot 142 in the beam can be designed to form a close fitting seal around the end of the truss.

Each truss 131 is supported at one end outside the charge end of the furnace by lifting mechanism 139 and at its opposite end by lifting mechanism 140 as shown in FIG. 12. Lifting mechanisms 139 and 140 are each comprised of an upper roller 146 supported by suitable brackets 147 mounted on a frame 148 extending across the width of the furnace. The frame 138 is supported at spaced intervals by a plurality of roller and bell-crank mechanisms 149 secured to a connecting rod 150 which turns in operated y suitable power means such as a hydraulic cylinder 151. Thus by means of the two lifting mechanisms the trusses 131 are all uniformly moved vertically across the width of the furnace.

Beams 144 supporting each refractory beam 141 are mounted on a plurality of roller and bell-crank mechanisms 153 each secured to a connecting rod 154 which in turn is operated by suitable power means such as hydraulic cylinder 155. A plurality of hydraulic cylinders and lifting mechanisms are provided under each refractory beam 141 across the width of the furnace and are coordinated to lift each refractory beam simultaneously. Moreover, during one phase of operation of the movable support members, the lifting mechanism for the refractory beams is coordinated with the lifting mechanism for the trusses, so that the refractory beams and the trusses may be lifted simultaneously at the same rate in a manner to be described fully hereinafter.

Each refractory beam and connected truss unit is moved longitudinally endwise of the furnace by suitable power means such as hydraulic cylinder 156 mounted on the bottom of the furnace by suitable support means and connected to the beams 144 underneath each refractory beam 141 by a suitable rocker arm mechanism 157 as shown in FIG. 12. The hydraulic cylinders 156 are all coordinated to move all of the refractory beams and trusses simultaneously longitudinally endwise of the furnace. Conventional water seals 158 are provided at the discharge end of each refractory beam and adjacent the inner end of each truss to prevent heat from escaping from the furnace as well as to prevent cold air from infiltrating into the furnace.

Referring to FiG. 11 a plurality of alloy bumper castings 161 are embedded in the refractory wall at the charge end of the furnace just above the hearth 124 to prevent incoming charges from striking the wall. Moreover, a plurality of hydraulic cylinders 162 are mounted in the same end wall just above the hearth to push charges at the charge end forwardly to tightly pack all the charges over the length of the trusses forming the first section of the movable charge supporting members of the hearth.

As shown in FIGS. 12 and 13, the bottom inner end of preheat zone 112 is provided with a plurality of downtake flues 165 operated at a negative pressure to cause the heated gases from the upper par of the preheat zone to move across the top of tightly packed charges to the charge end of the furnace and then down in the space between the charge end of the furnace and the end of the packed charges and subsequently to pass underneath the bottom of the charges to heat the bottoms thereof. The open framework of the movable trusses 131 greatly facilitates the passage of the heated gases around and underneath the charges. In this manner the charges are heated both on the top and on the bottom, thus eliminating an undesirable temperature difference between the top and the bottom of the charges which normally would cause the charges to warp. Moreover, the heated gases are more effectively utilized in that the cold charges extract heat from the combustion gas both on the top and on the bottom. The waste gases from the downtake flue 165 may be discharged out of the furnace through appropriate stack means.

One conventional operation of this embodiment of the invention utilizes billets 4 X 4 inches in size, although it is to be understood other types and sizes of charges may be heated in the furnace. Initially the refractory beams 141 and the trusses 131 are in a down position towards the discharge end. A pack of from four to six 4 X 4 inches billets are then charged through the charge opening in the side of the furnace whereupon they are supported by the skid pipes 125. The hydraulic cylinders 162 then push the pack of billets forwardly to tightly pack all the billets in the furnace over the length of the skid pipes 125 and the trusses 131 and to leave a space between the charge end of the furnace and the end of the tightly packed billets. The beams and trusses are then moved longitudinally endwise 8 inches 0 the charge end of the furnace and come to a rest position. At this point the beams and trusses are both simultaneously raised to lift all the charges in the furnace from the fixed supports of the hearth. The loaded beams and trusses then travel towards the discharge end of the furnace 4 inches and stop, whereupon the refractory beams 141 remain in a raised position while the trusses are lowered to cause the charges in the preheat zone to rest back on the fixed supports. in this position the raised refractory beams and he lowered trusses then travel an additional 4 inches toward the discharge end of the furnace and stop. The refractory beams then lower the charges back on the fixed supports of the hearth and return to their original lowered position whereupon the cycle is repeated.

Upon completion of the cycle the billets on the refractory beams 141 in the heating and soak zones have advanced 8 inches while the billets supported by the trusses 131 up to the point where the trusses enter the end of slots 142 at the end of refractory beams 141 have advanced 4 inches. Thus at the joint between the trusses and the ends of the refractory beams the closely packed adjacent billets are separated by the independent lowering motion of the trusses and are then spaced 4 inches part by the continuing 4 inches forward motion of the refractory beam as shown in FIG. 12. This 2:1 ratio stroke results in the billets passing through the furnace spending approximately 43 percent of the total time being heated on both the top and the bottom in the preheat zone 112 which occupies only 27 percent of the furnace length.

As the billets pass from the trusses 131 to the refractory beams 141 they continue to be conveyedthrough the furnace by the longitudinal and vertical motion of the refractory beams until they reach the discharge end 111 of the furnace from where the billets are then removed by conventional mechanism through a side discharge door.

It is to be understood that the invention is not limited to the particular embodiments described and shown, but that it includes any modifications and equivalents within the scope of the appended claims.

I claim:

1. A heating furnace comprising,

means defining a heating zone,

a charge supporting hearth,

said hearth including charge supporting members positioned substantially completely within said heating zone, each said charge supporting member comprising an upper tubular member, a lower tubular member and at least one intermediate tubular member extending between and alternately connected to said upper and lower tubular members in serpentine arrangement to form a rigid charge supporting truss having a rigid open framework throughout substantially its entire length,

means for supporting each of said charge supporting members,

and means for cooling each of said charge supporting members.

2. A heating furnace as defined in claim 1,

wherein said means for supporting each of said charge supporting members includes a plurality of spaced bottom partitions extending upwardly from the bottom of the furnace to define a series of bottom zones, said furnace further including heating means in at least one of said bottom zones.

3. A heating furnace as defined in claim 1,

wherein at least certain of said charge supporting members are movable both longitudinally endwise of the furnace and vertically in the furnace to convey a charge therethrough.

4. A heating furnace as defined in claim 3,

wherein said means for supporting said charge supporting members includes a plurality of bottom partitions extending upwardly from the bottom of said furnace and carriages on said partitions movable longitudinally endwise of the furnace.

5. A heating furnace as defined in claim 4,

wherein each carriage is movable in a slot in one of said partitions, said carriage overlapping the edges of said blot to form a traversing seal therewith.

6. A heating furnace as defined in claim 4,

which includes heating means mounted in at least some of said partitions underneath said charge supporting members for directing heat endwise of the furnace.

7. A heating furnace as defined in claim 1,

wherein a first series of said charge supporting members is mounted for longitudinal movement endwise of the furnace, a second series of said charge supporting members is mounted for vertical movement in the furnace, and means are provided for effecting longitudinal movement of said first series of said members and alternating vertical movement of said second series of said members to convey a charge through said zone.

8. A heating furnace as defined in claim 7,

wherein said means for supporting said charge supporting members includes a plurality of bottom partitions extending upwardly from the bottom of said furnace and carriages on said partitions mova ble longitudinally endwise of the furnace.

9. A heating furnace as defined in claim 8,

wherein each carriage is movable in a slot in one of said partitions, said carriage overlapping the edges of said slot to form a traversing seal therewith.

10. A heating furnace as defined in claim 8,

which includes heating means mounted in at least some of said partitions underneath said charge supporting members for directing heat endwise of the furnace.

1 1. A heating furnace comprising a plurality of spaced bottom partitions extending upwardly from the bottom of the furnace to define a series of bottom heating zones,

a plurality of charge supporting members constituting a hearth spanning said partitions and mounted thereon,

each of said charge supporting members comprising an upper tubular member, a lower tubular member, and an intermediate tubular member extending between and connected to said upper and lower tubular members to form i1 rigid charge supporting truss,

a first series of said charge supporting members being mounted for longitudinal movement endwise of the furnace,

a second series of said charge supporting members being mounted for vertical movement in the furnace,

carriage means mounting said first series of charge supporting members on said partitions,

means for cooling each of said charge supporting members,

heating means mounted in said partitions underneath said charge supporting members for directing heat endwise of the furnace, and

means for effecting longitudinal movement of said first series of charge supporting members and alternating vertical movement of said second series of charge supporting members to convey a charge through the furnace.

12. A heating furnace as defined in claim 11,

wherein said carriage means is movable in a slot in each said partition and overlaps the edges of said slot to form a traversing seal therewith.

13. A heating furnace as defined in claim 11,

which includes rollers mounted in said partitions for supporting said carriage means.

14. A heating furnace as defined in claim 11 which includes means for cooling said carriage.

15. A heating furnace as defined in claim 1 l,

which includes a discharge end, a bottom heating zone defined by said partitions adjacent said discharge end, heating means mounted in one of said partitions positioned to direct heat in the direction of travel of the charge in said bottom heating zone, and flue means adjacent said discharge end for collecting flue gas from said bottom heating zone.

16. A heating furnace comprising a plurality of spaced bottom partitions extending upwardly from the bottom of the furnace to define a series of bottom heating zones,

a plurality of charge supporting members constituting a hearth spanning said partitions and mounted thereon,

each of said charge supporting members comprising an upper tubular member, a lower tubular member, ad an intermediate tubular member extending between and connected to said upper and lower tubular members to form a rigid charge supporting truss,

at least certain of said charge supporting members being mounted for movement both longitudinally endwise of the furnace and vertically in the furnace,

carriage means mounting at least certain of said charge supporting members on said partitions,

means for cooling each of said charge supporting members,

heating means mounted in said partitions underneath said charge supporting members for directing heat endwise of the furnace, and

means effecting both longitudinal and vertical movement of at least certain of said charge supporting members to convey a charge through the furnace.

17. A heating furnace as defined in claim 16,

wherein said carriage means is movable in a slot in each said partition and overlaps the edges of said slot to form a traversing seal therewith.

18. A heating furnace as defined in claim 16,

which includes rollers mounted in said partitions for supporting said carriage means.

19. A heating furnace as defined in claim 16,

which includes means for cooling said carriage.

20. A heating furnace as defined in claim 16 wherein said charge supporting members mounted for movement both longitudinally and vertically in the furnace constitute a first series of charge supporting members and said furnace includes a second series of charge supporting members fixedly mounted therein.

21. A heating furnace as defined in claim 16,

which includes a discharge end, a bottom heating zone defined by said partitions adjacent said discharge end, heating means mounted in one of said partitions positioned to direct heat in the direction of travel of the charge in said bottom heating zone, and flue means adjacent said discharge end for collecting flue gas from said bottom heating zone.

22. A heating furnace having a charge end and a discharge end, comprising a plurality of spaced bottom partitions extending upwardly from the bottom of the furnace to define a series of bottom heating zones,

a plurality of charge supporting members constituting a hearth spanning said partitions and mounted thereon,

a final bottom heating zone defined by said partitions adjacent the discharge end of the furnace,

heating means mounted in one of said partitions underneath said charge supporting members in said final bottom heating zone and positioned to direct heat therethrough in the direction of travel of the charge, and

flue means adjacent the discharge end for collecting waste gas from said final bottom heating zone.

23. A heating furnace as defined in claim 22,

which includes means for operating said flue means at a negative pressure.

24. A heating furnace as defined in claim 23,

wherein said flue means is positioned between the discharge end of the furnace and said final bottom heating zone at a level below that of the charge supporting members.

25. A heating furnace comprising a charge supporting hearth,

said hearth including a plurality of movable charge supporting members,

each of said movable charge supporting members being comprised of a first section and a second section connected together at their inner ends and extending lengthwise of the furnace,

said first and second sections being mounted for movement both longitudinally endwise of the furnaceand vertically in the furnace,

said first and second sections being connected together to permit independent relative vertical movement with respect to each other,

said first section being comprised of an upper tubular member, a lower tubular member, and at least one intermediate tubular member extending between and connected to said upper and lower tubular members to form a rigid charge supporting truss,

means for cooling said first section, and

means for effecting both longitudinal movement of said first and second sections and independent relative vertical movement of said first and second sections with respect to each other to cause a charge to move through the furnace.

26. A heating furnace as defined in claim 25,

wherein an end portion of said first section is received in and is separately movable vertically in a slot in said second section to cause a plurality of charges packed together on said first section to become spaced as the charges are conveyed from said first section to said second section.

27. A heating furnace as defined in claim 26, 

1. A heating furnace comprising, means defining a heating zone, a charge supporting hearth, said hearth including charge supporting members positioned substantially completely within said heating zone, each said charge supporting member comprising an upper tubular member, a lower tubular member and at least one intermediate tubular member extending between and alternately connected to said upper and lower tubular members in serpentine arrangement to form a rigid charge supporting truss having a rigid open framework throughout substantially its entire length, means for supporting each of said charge supporting members, and means for cooling each of said charge supporting members.
 1. A heating furnace comprising, means defining a heating zone, a charge supporting hearth, said hearth including charge supporting members positioned substantially completely within said heating zone, each said charge supporting member comprising an upper tubular member, a lower tubular member and at least one intermediate tubular member extending between and alternately connected to said upper and lower tubular members in serpentine arrangement to form a rigid charge supporting truss having a rigid open framework throughout substantially its entire length, means for supporting each of said charge supporting members, and means for cooling each of said charge supporting members.
 2. A heating furnace as defined in claim 1, wherein said means for supporting each of said charge supporting members includes a plurality of spaced bottom partitions extending upwardly from the bottom of the furnace to define a series of bottom zones, said furnace further including heating means in at least one of said bottom zones.
 3. A heating furnace as defined in claim 1, wherein at least certain of said charge supporting members are movable both longitudinally endwise of the furnace and vertically in the furnace to convey a charge therethrough.
 4. A heating furnace as defined in claim 3, wherein said means for supporting said charge supporting members includes a plurality of bottom partitions extending upwardly from the bottom of said furnace and carriages on said partitions movable longitudinally endwise of the furnace.
 5. A heating furnace as defined in claim 4, wherein each carriage is movable in a slot in one of said partitions, said carriage overlapping the edges of said blot to form a traversing seal therewith.
 6. A heating furnace as defined in claim 4, which includes heating means mounted in at least some of said partitions underneath said charge supporting members for directing heat endwise of the furnace.
 7. A heating furnace as defined in claim 1, wherein a first series of said charge supporting members is mounted for longitudinal movement endwise of the furnace, a second series of said charge supporting members is mounted for vertical movement in the furnace, and means are provided for effecting longitudinal movement of said first series of said members and alternating vertical movement of said second series of said members to convey a charge through said zone.
 8. A heating furnace as defined in claim 7, wherein said means for supporting said charge supporting members includes a plurality of bottom partitions extending upwardly from the bottom of said furnace and carriages on said partitions movable longitudinally endwise of the furnace.
 9. A heating furnace as defined in claim 8, wherein each carriage is movable in a slot in one of said partitions, said carriage overlapping the edges of said slot to form a traversing seal therewith.
 10. A heating furnace as defined in claim 8, which includes heating means mounted in at least some of said partitions underneath said charge supporting members for directing heat endwise of the furnace.
 11. A heating furnace comprising a plurality of spaced bottom partitions extending upwardly from the bottom of the furnace to define a series of bottom heating zones, a plurality of charge supporting members constituting a hearth spanning said partitions and mounted thereon, each of said charge supporting members comprising an upper tubular member, a lower tubular member, and an intermediate tubular member extending between and connected to said upper and lower tubular members to form i1 rigid charge supporting truss, a first series of said charge supporting members being mounted for longitudinal movement endwise of the furnace, a second series of said charge supporting members being mounted for vertical movement in the furnace, carriage means mounting said first series of charge supporting members on saId partitions, means for cooling each of said charge supporting members, heating means mounted in said partitions underneath said charge supporting members for directing heat endwise of the furnace, and means for effecting longitudinal movement of said first series of charge supporting members and alternating vertical movement of said second series of charge supporting members to convey a charge through the furnace.
 12. A heating furnace as defined in claim 11, wherein said carriage means is movable in a slot in each said partition and overlaps the edges of said slot to form a traversing seal therewith.
 13. A heating furnace as defined in claim 11, which includes rollers mounted in said partitions for supporting said carriage means.
 14. A heating furnace as defined in claim 11 which includes means for cooling said carriage.
 15. A heating furnace as defined in claim 11, which includes a discharge end, a bottom heating zone defined by said partitions adjacent said discharge end, heating means mounted in one of said partitions positioned to direct heat in the direction of travel of the charge in said bottom heating zone, and flue means adjacent said discharge end for collecting flue gas from said bottom heating zone.
 16. A heating furnace comprising a plurality of spaced bottom partitions extending upwardly from the bottom of the furnace to define a series of bottom heating zones, a plurality of charge supporting members constituting a hearth spanning said partitions and mounted thereon, each of said charge supporting members comprising an upper tubular member, a lower tubular member, ad an intermediate tubular member extending between and connected to said upper and lower tubular members to form a rigid charge supporting truss, at least certain of said charge supporting members being mounted for movement both longitudinally endwise of the furnace and vertically in the furnace, carriage means mounting at least certain of said charge supporting members on said partitions, means for cooling each of said charge supporting members, heating means mounted in said partitions underneath said charge supporting members for directing heat endwise of the furnace, and means effecting both longitudinal and vertical movement of at least certain of said charge supporting members to convey a charge through the furnace.
 17. A heating furnace as defined in claim 16, wherein said carriage means is movable in a slot in each said partition and overlaps the edges of said slot to form a traversing seal therewith.
 18. A heating furnace as defined in claim 16, which includes rollers mounted in said partitions for supporting said carriage means.
 19. A heating furnace as defined in claim 16, which includes means for cooling said carriage.
 20. A heating furnace as defined in claim 16 wherein said charge supporting members mounted for movement both longitudinally and vertically in the furnace constitute a first series of charge supporting members and said furnace includes a second series of charge supporting members fixedly mounted therein.
 21. A heating furnace as defined in claim 16, which includes a discharge end, a bottom heating zone defined by said partitions adjacent said discharge end, heating means mounted in one of said partitions positioned to direct heat in the direction of travel of the charge in said bottom heating zone, and flue means adjacent said discharge end for collecting flue gas from said bottom heating zone.
 22. A heating furnace having a charge end and a discharge end, comprising a plurality of spaced bottom partitions extending upwardly from the bottom of the furnace to define a series of bottom heating zones, a plurality of charge supporting members constituting a hearth spanning said partitions and mounted thereon, a final bottom heating zone defined by said partitions adjacent the discharge end of the furnace, heating means mounted In one of said partitions underneath said charge supporting members in said final bottom heating zone and positioned to direct heat therethrough in the direction of travel of the charge, and flue means adjacent the discharge end for collecting waste gas from said final bottom heating zone.
 23. A heating furnace as defined in claim 22, which includes means for operating said flue means at a negative pressure.
 24. A heating furnace as defined in claim 23, wherein said flue means is positioned between the discharge end of the furnace and said final bottom heating zone at a level below that of the charge supporting members.
 25. A heating furnace comprising a charge supporting hearth, said hearth including a plurality of movable charge supporting members, each of said movable charge supporting members being comprised of a first section and a second section connected together at their inner ends and extending lengthwise of the furnace, said first and second sections being mounted for movement both longitudinally endwise of the furnace and vertically in the furnace, said first and second sections being connected together to permit independent relative vertical movement with respect to each other, said first section being comprised of an upper tubular member, a lower tubular member, and at least one intermediate tubular member extending between and connected to said upper and lower tubular members to form a rigid charge supporting truss, means for cooling said first section, and means for effecting both longitudinal movement of said first and second sections and independent relative vertical movement of said first and second sections with respect to each other to cause a charge to move through the furnace.
 26. A heating furnace as defined in claim 25, wherein an end portion of said first section is received in and is separately movable vertically in a slot in said second section to cause a plurality of charges packed together on said first section to become spaced as the charges are conveyed from said first section to said second section. 